More than 60,000 women are hospitalized in the U.S. each year with a benign ovarian tumor. The cumulative incidence by age 60 is 3%. There is almost no information about the distribution of these tumors in any population. There is speculation, but no evidence, as to whether some of these tumors are precursors of ovarian cancer. The objective of this case-control study is to identify risk factors for the major histopathological types of these tumors. Those factors that are associated with ovarian cancer are of primary importance in this investigation. Additional goals are to identify and compare the risk factors for the several histopathologic subtypes. Of secondary interest is whether aspects of care-seeking behavior influence risk of diagnosis or are related to tumor size at diagnosis. We plan to identify about 1300 women aged 18 to 74 who have a pathologically confirmed benign ovarian tumor in any of five hospitals from January, 1991 through December, 1992 (24 months). We expect to complete in-person interviews with about 1000 cases, including at least 330 women who has a mature teratoma, 190 women who had an endometrioma, and 460 women who had one of the following benign epithelial tumors: serouscystadenoma, mucinouscystadenoma, or fibroadenoma. We plan to interview about 545 community controls who will be identified using random digit dialing techniques. Analysis will include calculation of odds ratios with confidence intervals, followed by stratified and multivariate analyses using logistic regression techniques. Analyses will be performed separately for each of the major tumor types, and will be stratified by the usual frequency and source of gynecological care.